The Australian cotton industry still relies on repeated applications of synthetic pesticides to manage pests in crops. Accompanying problems associated with insecticide resistance, disruption of beneficial species, high cost of production, and environmental impact now require that alternative strategies be investigated for managing Helicoverpa spp. These include (but are not limited to) genetically engineered cotton crops containing insecticidal protein of Bacillus thuringiensis (Bt) and other host plant resistances, biopesticides, better management of beneficial species, trap crops, intercropping and companion planting, and manipulation of the behaviour of pests and beneficial insects. Genetically engineered (transgenic) crops are now grown in Australia and many countries to control lepidopteran pests and their introduction has reduced synthetic insecticide use against these pests. However, other pests are not affected by the toxin in the transgenic plants e.g. sucking pests. Also third to late stage Helicoverpa larvae that can tolerate the toxin have led to increased use of synthetic insecticides to control them on both transgenic and conventional cotton crops. Thus the need to develop new approaches to manage these pests is crucial.
One of the approaches with greater potential to revolutionalise the way insect pests are managed in broadacre crops such as cotton, is the use of natural plant chemical compounds or plant extracts. The natural plant extracts or secondary plant compounds (SPCs) in general can influence the behaviour of insects by functioning as cues stimulating an insect's “interest” or deter insects from infesting a particular host plant (Rhoades and Coates 1976). Many SPCs have evolved in plants to actually protect the plants against pest infestation (Rhoades and Coates 1976). This has led to several examples of SPCs being used as botanical insecticides to reduce pest damage when applied to crop plants. Some SPCs extracted from non-host plants and then sprayed on host plants can change the behaviour of a pest, particularly moths, which then avoid the host plant (Tingle and Mitchell 1984). Numerous studies into pest management have focussed on chemical compounds that kill the pest rather than behaviour modifying compounds (Tingle and Mitchell 1984, Mensah and Moore, 1999). Consequently, potentially useful compounds with more subtle modes of action that could lead to novel products have been overlooked (Mensah and Moore, 1999). Such compounds attract or repel pests over considerable distances; or stimulate or deter both feeding and egg-laying following contact. Deterrent compounds directly suppress oviposition and feeding by insects (Mensah, 1996, Mensah et al. 2000), they are considered more important than stimulants and in fact a deterrent effect is more commonly noted in SPCs (Bernays and Chapman 1994). It is plausible that the efficacy of a deterrent would be increased when used in combination with an attractant/stimulant applied to a non-valued resource (Miller and Cowles, 1990) in a push-pull strategy (Pyke et al. 1987). Therefore, a tool to modify egg laying and/or feeding behaviour of insect pests is a novel approach to pest management in agricultural crops and offers potentially very significant benefits.